Separate event class factory module.

src/js/lib/event-class.js

@@ -0,0 +1,17 @@
+/* Copyright (c) 2015 Hyunje Alex Jun and other contributors
+ * Licensed under the MIT License
+ */
+'use strict';
+
+var incrementingId = 0;
+module.exports = function () {
+  var id = incrementingId++;
+  return function (eventName) {
+    var className = '.perfect-scrollbar-' + id;
+    if (typeof eventName === 'undefined') {
+      return className;
+    } else {
+      return eventName + className;
+    }
+  };
+};